Britannica Learning Library 002 - Planet Earth

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CAVES • GEOGRAPHY • RIVERS

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G R A N D C A N Y O N

How does the ocean help plants to grow?

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O C E A N S

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small to hold even a house. The largest islands contain whole countries.

If you live in England, Iceland, Australia, or Japan, you live on an island. But these islands are so large that you might walk all day and never see water.

How do islands develop in the first place?

Some islands begin as fiery volcanoes in the ocean. Hot lava pours out of the volcano, making the island bigger and bigger. Slowly, as the lava cools,

it becomes solid land, and when it rises above the water, it becomes an island. These are the volcanic islands.

Other islands are actually parts of the world’s continents. Some of the land toward the edge of the continent may have been worn away over many, many years by wind or rain, or perhaps some of it sank. Then water from the ocean filled the low places and made a new island.

A row of islands may once have been the tops of mountains in a mountain range. The Aleutian Islands off the coast of North America were probably once a part of a mountain range that connected Alaska with Asia.

Maybe most surprising are the islands that are built up from the bottom of the ocean from the skeletons of tiny sea animals called “coral.” As some corals die, others live on top of them. After thousands of years a coral island rises to the ocean surface. And these islands go on living!

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GREAT BARRIER REEF • OASIS • PENINSULAS

This photo from the air shows one of the islands of the Maldives, a country made up of about 1,200 islands in the Indian Ocean.

© Lawson Wood/Corbis

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I S L A N D S

Giant lizards that look like dragons!

These are only a few of the special things that make the Galapagos Islands different from any other place on Earth. The islands lie in the Pacific Ocean, far away from any other land. People have called them “the world’s end.” Together with other natural wonders, the Galapagos are a World Heritage site.

The Galapagos Islands were formed from volcanoes that erupted in the sea. The bare and rocky islands look as if no creature could ever live there. But thousands of animals do, including many found nowhere else in the world. One animal that lives there is the giant tortoise, or land turtle. In fact, the islands got their name from these tortoises. The word galápagos means “tortoises” in Spanish.

The Galapagos Islands were especially important to the famous English scientist Charles Darwin. When Darwin visited the islands, he discovered that there were creatures living there that did not live anywhere else in the world. He saw three-foot-long lizards—land iguanas that looked like small dragons. And he saw amazing marine iguanas, lizards that had actually learned to swim. He also found a great many birds called

“finches” that were all much the same except for differences in their beaks. These differences meant that they all ate different things, which allowed them all to share the same habitat.

Darwin decided that all plants and animals evolve, or change little by little, as the world around them changes. One plant or animal group will usually be more successful than another. Darwin called this process “natural selection.” And he called the overall change through time the “theory of evolution.”

Do you think people are evolving? What do you think we might look like in a million years?

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GEOGRAPHY • ISLANDS • PACIFIC OCEAN

The giant Galapagos tortoise can live as long as 150 years—longer than almost any other animal. Sadly, few are left today.

© Craig Lovell/Corbis

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G R E A T B A R R I E R R E E F